Cocoa: fix backend since recent changes
Cocoa: fix backend since recent changes

Before, the window size was given at its creation. Now, it's done at
the drawing step because it's only relevant when there is a glimagesink
element in the pipeline.

ystreet/gst-plugins-gl,mapmapteam/gst-plugins-gl,mapmapteam/gst-plugins-gl,ystreet/gst-plugins-gl,mapmapteam/gst-plugins-gl,ystreet/gst-plugins-gl